Substantial savings of time and money have been realized in the industry by handling a plurality of printed circuit boards (PCB's) while they are still interconnected in a panel of substrate material. Better utilization is realized with this approach in such processing as population of the PCB's with components, wave soldering of the populated boards, and quality control such as electrical function testing of whole boards or selected components, particularly when considering the automated processing demands of today's industry.
Methods presently used for separating each unpopulated or prepopulated panel into plural, individual PCB's include: shearing; routing; and the "break-away" methods of routing with tabs; scoring; perforation; and punch-back.
Routing with tabs comprises routing slots in the panel (while leaving spaced support tabs) to define the perimeters of the individual boards, so that the tabs may be cut or broken in order to perform board separation.
Scoring comprises grooving board perimeters on at least one side of the panel in order to effect board separation by breaking along the score-lines.
Perforation comprises drilling a series of closely spaced holes in the panel along the board perimeters so that board separation is performed by breaking along the lines of perforations.
The punch-back method utilizes a custom-made die to punch each board out of the panel and then pull it back into the panel so that, after population, the boards are easily pushed from the panel.
"Break-away" methods of preparing panels for subsequent separation of the populated PCB's, inherently rob the panel of its rigidity. Consequently, the panels are prone to sagging during wave soldering, excessive warping, and premature breakage prior to subsequent separation into individual circuit boards. Moreover, methods incorporating excessive treatment by a router are expensive, can permit solder to overflow onto the component side of the panel during wave soldering, and often can require a secondary procedure for removing tab stubs. Perforation and scoring yield poor quality edges and cannot hold close tolerances. Punch-back methods require expensive tooling and cannot process zero-spaced configurations, i.e., panels without scrap strips between adjacent circuit boards. Premature separation during panel handling is frequently encountered with the punch-back and scoring methods.
Whether or not the boards have been populated, high precision shearing and routing are recognized as preferred, cost-effective methods for PCB profiling by separating individual boards from the panels. The shock to delicate components and traces, normally encountered during the separating of boards from panels by breaking along perforation or score lines, can be obviated by use of router bits and shearing blade configurations. Further, a panel may be gently sheared or routed without the shock of other methods, while providing excellent edge quality and holding board perimeter tolerances within 0.005 inches, repeatedly. Since there are no tab stubs to be removed with the shearing method, the circuit boards often can be zero-spaced (without waste strips) in order to provide more boards per panel. So called external, straight cuts can be performed by shearing in less time than it takes to cut the same run with an NC router, while routing can provide internal, irregular, and curvilinear cuts which can not be accomplished with shearing. Thus, routing and shearing can be combined in order to minimize the routing time and maximize panel rigidity. The clean edges provided by shearing and routing also enhance computer aided design and manufacturing (CAD/CAM).
One presently used method of routing prepopulated panels in order to separate them into individual circuit boards has the router positioned on the same side of the substrate as the component bodies during the routing, thus presenting several problems which the instant invention overcomes. For instance, this prior art method is limited by the height of the components when it is necessary for a thin cut to be made in the substrate between two closely spaced components and at least one of the components is over one inch in height. A router bit which is sufficiently long and small in diameter to accomplish such a cut is too unstable, flexible, and fragile. Further, areas of the circuit board which are overhung by components, or portions of certain components, are shielded from overhead operation by the prior art routing arrangement. This prior art also requires that the panels are laying on a flat surface, which must be cork board or the like in order to accommodate the leads protruding from the bottom side thereof such that the board is flat to the surface.
The instant invention is particularly directed to the method and apparatus for automated handling of panels comprising a plurality of interconnected substrates in order to control and separate the circuit boards in a continuous processing line.
One embodiment incorporates both routing and shearing at a cutting station through which an individual or multiboard panel is fed, with the board being at any of three different levels at the cutting station and above the router. At a lowest level, the board rests on a fixed lower die for shearing by a movable shearing blade. A mid-level allows the downwardly protruding leads of components on the board to clear the fixed die during feeding of the board, while still allowing routing of the board during such feeding. The highest level allows lateral positioning of the router for plunge cuts and the like, without board interference.
Another embodiment provides for routing of a circuit board, with or without shearing, wherein the router is positioned on the "bottom" or opposite side of the substrate from the "top" or component body side. Thus, component heights and overhangs do not limit the router cuts.
Throughout the handling of the panels and panel portions, sensing, gripping, and indexed feeding of the panels and panel portions are under the control of a programmable computer.